The invention concerns a single tracked two-wheeled vehicle in particular a bicycle, an electrical bicycle, an electrical scooter or a motorized scooter consisting essentially of a front portion and a rear portion connected to each other for pivoting by means of a pivot mechanism disposed approximately in the middle position between the front and the rear wheels, wherein the front portion comprises a front wheel suspension with the front wheel, a handle bars displaced relative to the pivot mechanism in the forward direction and a connection element for the handle bars, and the rear portion comprises a rear wheel suspension with the rear wheel and a saddle support bearing the saddle, and a drive unit is provided for belonging to either the front portion or the rear portion. A two-wheeled vehicle of this kind is disclosed in the publication DE 98366 C1.
The majority of conventional single track two-wheeled vehicles, whether they are bicycles, motorcycles or motor scooters, have a steering geometry with trailing action of the front wheel. The extension of the pivot axis joining the rear frame portion with the front fork and the handle bars has a point of intersection with the path of the vehicle which is situated several centimeters in front of the seating position of the front wheel. This trailing action effects a more stable straight travel for the two-wheeled vehicle. Every steering system for a single track two-wheeled vehicle has two contact surfaces with the travel path at the seating surfaces of the front and the rear wheels. Conventional two-wheeled vehicles effect steering of the vehicle through operation of the handle bars which are connected to and rotate together with the fork and the front wheel. Another measure influencing the stability of the vehicle is a displacement between the pivot axis and the front wheel axis. This displacement effects a slight lifting of the head of the fork during steering causing a restoring force leading to a more stable straight line dependence for the two-wheeled vehicle. When driving around curves, the operator must displace his weight and a tilting of the two-wheeled vehicle is required in order to effect a new equilibrium state compared to the initial situation. The equilibrium position thereby depends on the degree of steering of the front wheel relative to the rear wheel, the speed, and the weight of the operator. The non-centered disposition of the common pivot axis of the front and the rear frame units facilitates easy steering of a single track two-wheeled vehicle but has however associated problems.
The asymmetric configuration of the pivot axis in a single track two-wheeled vehicle of conventional construction causes the front and rear wheels to have a differing tilt with respect to the path traveled when going around a curve. This has, among other things, the consequence that unnecessary frictional forces occur during steering resulting e.g. in uneven wear on the tread surfaces of the front and rear wheels. A further aspect affecting the safety of the vehicle concerns the position of the wheels in curves. In curves, neither the front nor the rear wheel assume a perfect position for traveling through the curve. An optimum wheel position would be tangent to the curve with an equal tilt for both wheels. Traveling through curves in conventional two-wheeled vehicles therefore entails a danger of falling, in particular on slippery surfaces. In the event of insufficient friction between the wheels and the underlying surface, the steering acting on the front wheel alone leads to skidding of the front wheel and to crashing. Acceleration and braking in a curve can lead to skidding of the rear wheel and thereby also cause a crash. An additional disadvantage of conventional bicycles is evident during uphill travel. The increased pedal forces necessary thereby lead to compensation reactions on the steering wheel as result a of which the front wheel is deflected back and forth. This leads to a path which is not straight as well as to increased friction between the front wheel and the underlying surface. The uneven weight distribution on the front and rear wheels caused by the asymmetric configuration of the frame of conventional two-wheeled vehicles leads to additional loads on the frame which e.g. must be accepted by structures which are stiff when subjected to torques.
A single track two-wheeled vehicle categorizing the invention is disclosed in German patent DE 98366 C.
This patent describes a single track two-wheeled vehicle having a pivot axis disposed between a front and a rear wheel which is tilted in a forward direction and displaced from the middle towards the front. With this two-wheeled vehicle, the connecting element bearing the handlebars is borne for rotation in the front part of the frame. The steering motion of the handlebars is transferred to the rear frame portion via two circular segment shaped toothed racks. This configuration does not allow balanced deflection of the front and rear frame portions. The rotating bearing of the handlebars in the front frame member prevents direct transfer of steering motion from the front to the rear frame portion.
A bicycle has become known in the art by means of French patent 982,683 which can be transformed into a cart in a simple manner. In correspondence with this purpose, this bicycle has two vertical axes which are disposed on the left and the right of a central frame portion and which allow the front and the rear portions of the frame to pivot through 90.degree. so that a single axis two-track cart is created. This configuration does not allow the pivot axis to be in a central position. The steering does not act equally on both wheels.
The so-called FLEVO-bike represents a current development as described in the magazine "Radfahren EXTRA" [Bike-riding EXTRA] 4.92. This bicycle also has a pivot in an approximately middle position between the front and the rear wheel. This pivot mechanism is however tilted to such a strong extent in the backward direction that the pivot axis intersects the vehicle path in front of the seating position of the front wheel. The stability of this bicycle is therefore realized through trailing action. In addition, the pedals form a non-rotating unit together with the front frame portion so that the steering capability of such a reclining operator bicycle is extremely limited.